Fish eye lens system

ABSTRACT

An improved compact high-speed fish eye lens system with minimal saggital flare is provided. The lens system comprises a front lens group having a pair of negative meniscus lens elements convex to the object side, an intermediate lens group having a pair of positive lens elements and a negative lens element, a rear lens group having a pair of doublets, the object side one of which includes an intermediate cemented surface having a positive refractive power. The radius of curvature, R, of the intermediate cemented surface of the object side doublet fulfills the following conditions wherein f represents the focal length of the whole lens system: 
     f&lt;R&lt;3f

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a fish eye lens system having anextreme wide field angle reaching 180 degrees, and more particularly toa fish eye lens system having both high speed and a compact size.

2. Description of the Prior Art

In the field of photography, there have been known various types of fisheye lens systems for 35 millimeter SLR cameras, such as disclosed inU.S. Pat. Nos. 3,734,600, 4,009,943, and Japanese Patent ApplicationLaid-Open No. 54-32319 on Mar. 9, 1979.

A fish eye lens system for use in 35 mm SLR cameras generally has afront lens group of a far greater negative refractive power than that ofan ordinary inverted telephoto type wide angle lens system since afairly large back focal distance, relative to the focal length of thewhole lens system, is required for avoiding an increase in size of thelens system. This extreme power distribution is apt to cause fieldcurvature and astigmatism in the transmitted image. In addition,sagittal flare including Rinnen fehler is also increased if a high speedsuch as F/2.8 is desired.

To improve the field curvature and astigmatism, it is basicallynecessary to avoid any negative deviation of the Petzval sum to thegreatest extent possible. In the prior art, this has been generallyattempted by providing, at the image side of the aperture stop, at leastone doublet composed of a positive lens element of alow-refractive-index-low-dispersion glass and a negative lens element ofa high-refractive-index-high-dispersion glass with a cementedintermediate surface of a suitable negative refractive power formedtherebetween. This approach helps avoid significant negative deviationof the Petzval sum plus also permitting correction of chromaticaberration.

The conventional lens design has taught that an additional one or moredoublet, similar to the above-mentioned doublet, should be furtherprovided on the image side of the aperture stop, alternatively thedifference in the refractive index on the opposite sides of the cementedsurface of the above-mentioned doublet could be increased if a stillgreater increase of negative refractive power in the front lens group isdesired for making the lens system even further compact. Theconventional lens design has also suggested forming the negative lenselements in the front lens group out of a glass of as high refractiveindex as possible to also reduce the size of the lens system.

With respect to the previously mentioned sagittal flare which includesRinnen fehler, the conventional lens design for an extremely wide anglehigh speed lens system has permitted this aberration to remain if thedesire for compactness is a preferred design criterion. This is becauseof the following reasons. The sagittal flare is generally a typical andfatal aberration to a lens system of high speed, and is moreparticularly remarkable in a case of a Gauss type lens system or aninverted telephoto type wide angle lens system. For correcting thisaberration, it may be recommended to avoid locating a refracting surfacehaving a short negative radius of curvature at a position in which anoff axial light pencil passes the surface apart from the optical axis.An example of such a design technique for this purpose would be to use aglass of high refractive index for increasing the radius of curvature asmuch as possible. However, in case of an extremely wide angle lenssystem of a compact size having a field angle greater than 72 degreesand a high speed greater than F/2.8, the degree of freedom in designingthe lens system is greatly restricted and a practical way tosufficiently correct the sagittal flare is still a design goal. Thus,the sagittal flare has been generally permitted to remain to somedegree, and it has been excused on the basis that the remaining sagittalflare can vanish if the aperture stop is stopped down to a size withwhich photography is most frequently practised.

The prior art is still seeking a compact fish eye lens with minimalsagittal flare.

SUMMARY OF THE INVENTION

An object of the present invention is to provide a compact and highspeed fish eye lens system having a front lens group of a relativelygreat negative refractive power in which the sagittal flare, includingRinnen fehler, as well as the field curvature and the astigmatism issufficiently corrected.

Another object of the present invention is to provide the above fish eyelens system in a compact design expressed by the following conditions:

2.7<Σd/f<3.1

2.4<D₁ /f<2.7

wherein:

Σd represents the total length of the whole lens system;

D₁ represents the diameter of the clear aperture of the front lenselement of the lens system, and

f represents the focal length of the whole lens system.

Each of the embodiments of the fish eye lens system of the presentinvention comprises a front lens group consisting of a pair of negativemeniscus lens elements, both convex to the object side, an intermediatelens group consisting of a pair of positive lens elements and a negativelens element and a rear lens group consisting of a pair of doublets, theobject side of one doublet includes an intermediate cemented surfacehaving a positive refractive power.

The features of the present invention which are believed to be novel areset forth with particularity in the appended claims. The presentinvention, both as to its organization and manner of operation, togetherwith further objects and advantages thereof, may be best understood byreference to the following description, taken in conjunction with theaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 represents a schematic view of a first embodiment of the presentinvention;

FIGS. 2a, 2b and 2c represent graphic plots of the various aberrationsof the first embodiment;

FIG. 3 represents a schematic view of a second embodiment of the presentinvention;

FIGS. 4a, 4b and 4c represent graphic plots of the various aberrationsof the second embodiment;

FIG. 5 represents a schematic view of a third embodiment of the presentinvention;

FIGS. 6a, 6b and 6c represent graphic plots of the various aberrationsof the third embodiment;

FIG. 7 represents a schematic view of a fourth embodiment of the presentinvention;

FIGS. 8a, 8b and 8 c represent graphic plots of the various aberrationsof the fourth embodiment;

FIG. 9 represents a schematic view of a fifth embodiment of the presentinvention; and

FIGS. 10a, 10b and 10crepresent graphic plots of the various aberrationsof the fifth embodiment.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The following description is provided to enable any person skilled inthe optical art to make and use the invention and sets forth the bestmodes contemplated by the inventor for carrying out his invention.Various modifications, however, will remain readily apparent to thoseskilled in the art, since the generic principles of the presentinvention have been defined specifically to provide an improved compacthigh-speed fish eye lens system.

The derivation of the formula and the relationship set forth herein canbe accomplished with the assistance of a computer. The present inventionrepresents the parameters of a compromise balance of acceptableaberrations in a relatively easily manufactured and low-cost compactlens system for utilization, for example, with a single lens reflexcamera.

In each of the schematic cross sectional views in the figures, the lensgroups have been designated by a Roman numeral to simply establish thefirst, second and third lens groups that are traditionally associatedwith the design of a fish eye lens system.

The improved compact fish eye lens system of the present inventionprovides an optimized optical lens design with a choice of certainparameters set forth herein to solve the problems of spherical andlateral chromatic aberrations, distortion, and astigmatism experiencedwith a field angle of 180 degrees. The present invention is particularlydesigned to remove the problems of sagittal flare that have beentraditionally experienced with fish eye lens systems, particularly of acompact configuration.

Each of the embodiments of the present invention provide an apertureratio of F/2.8 and a back focal length of slightly greater than twotimes the focal length of the system. Further, each of the embodimentsare particularly adapted for use on a compact 35 mm. SLR camera.

With reference to the schematic cross sectional views of the embodimentsof the present invention, it can be seen that a minimal number of lensesare utilized to accomplish the purpose of the present invention tothereby ensure a lightweight compact lens design. The lenses are furtherdesignated in groups with a first lens group, I and a second lens group,II, positioned on the object side of a diaphragm while a third lensgroup, III, is positioned on the image side of a diaphragm. As can beseen from the figures, a filter element can be positioned in the lenssystem, such as before the diaphragm and can be either staticallypositioned or capable of being optionally changed, as desired.

The Tables subsequently provided herein will establish the particulardimensions and parameters of the individual lens elements that make upeach of the improved fish eye lens systems in such a manner that anyoneskilled in the optical arts can reproduce the invention. These Tables,however, should not be construed as limiting to the generic designprinciples that are disclosed herein.

In the accompanying drawings which supplement the Tables, the lenses, inaccordance with the present invention, are illustrated diagrammaticallywith light assumed to travel from left to right. The radii of curvatureof the lenses are indicated by, r, with a subscript corresponding to theconsecutive numbers of the lens element surfaces. The axial spacings, d,along the optical axis include both the axial spacings between the lenselements and the thickness of the lens elements, again with a subscriptindicating a spatial position in the lens system. The minus signsindicate surfaces concave toward the object side, while the surfaceswithout the sign are convex toward the object side. All lineardimensions are given in absolute values and are given with reference tothe equivalent focal length of unity. The Tables also provide, withrespect to each example, the intended relative aperture, the total angleof view, 2ω, the back focus or back focal length with reference to anobject at infinity, the refractive index and the Abbe number.

As is apparent from FIGS. 1, 3, 5, 7 and 9, the fish eye lens system ofthe present invention comprises a front lens group (I) consisting of apair of negative meniscus lens elements both convex to the object side,an intermediate lens group (II) consisting of a pair of positive lenselements and a negative lens element, and a rear lens group (III)consisting of a pair of doublets, the object side one of which includesan intermediate cemented surface (r₁₃ in FIGS. 1, 5 and 9; or r₁₂ inFIGS. 3 and 7) having a positive refractive power Φ. According to thepresent invention, the radius of curvature R of the intermediatecemented surface of the object side doublet in the rear lens groupfurther fulfills the following condition if f represents the focallength of the whole lens system:

f<R<3f

As shown in the drawings, the lens system according to the presentinvention further comprises an aperture stop (S) and an exchangeablefilter (F) both located between the intermediate and rear lens groups.

In some of the embodiments of the present invention as in FIGS. 1, 5 and9, one of the pair of positive lens elements is cemented to the negativelens element in the intermediate lens group (II), the other of the pairof positive lens elements being located at the image side of thecemented lens elements such as in the case of the FIG. 1 embodiment,while at the object side of the cemented lens elements in case of theembodiment in FIGS. 5 or 9. All of the three lens elements are cementedtogether in the intermediate lens group (II) in case of the embodimentsin FIGS. 3 and 7.

As already mentioned, a fish eye lens system for 35 mm. SLR camerasgenerally requires a fairly great back focal distance relative to thefocal length of the whole lens system to allow the reflex mirror to flipup and down freely. The fish eye lens system according to the presentinvention also has a back focal distance greater than the focal lengthof the whole lens system.

With respect to the front lens group (I) of the present invention, apair of negative meniscus lens elements both convex to the object sideare designed to create a relatively great negative refractive power asdefined within the following range:

2.7<|f_(I) |/f<3.1

wherein, f_(I) represents the focal length of the front lens group. Forcreating such a great negative refractive power, a front lens groupconsisting of three or more lens elements would be generally favorablefor aberration correction. According to the present invention, however,a pair of negative lens elements, which correspond to an expedientlysimple lens construction for the front lens group, is successfullycombined with the intermediate and rear lens groups of the presentinvention to permit the inventive design to be compact in size and lowin cost.

The intermediate lens group (II) includes at least one cemented surfacebetween a negative lens element of low dispersion and a positive lenselement of high dispersion cemented thereto for correcting lateralchromatic aberration in cooperation with the cemented surface of theimage side doublet in the rear lens group (III). The refractive power ofthe cemented surface in the intermediate lens group (II) is negative forcorrecting field curvature and astigmatism. The other one of the pair ofpositive lens elements in the intermediate lens group (II) is locatedapart from the doublet to form an air space therebetween as in FIGS. 1,5 and 9 or can be further cemented to the doublet to form a secondcemented surface therebetween as in FIGS. 3 and 7. This air space, orthe second cemented surface, has a positive refractive power for mainlycorrecting the negative coma caused by the first lens group (I) and thefirst mentioned cemented surface in the intermediate lens group (II),and additionally for reducing sagittal flare including Rinnen fehler.The refractive power of the whole intermediate lens group (II) isrecommended to be within the following range:

2.6<f_(II) /f<3.1

wherein, f_(II) represents the focal length of the whole second lensgroup (II).

With respect to the rear lens group (III), the object side doubletfunctions to remove sagittal flare including Rinnen fehler. On thecontrary, the image side doublet in the rear lens group (III) is usedfor avoiding any negative deviation of the Petzval sum and for furthercorrecting chromatic aberration by means of a combination of a positivelens element of a low-refractive-index-low-dispersion glass and anegative lens element of a high-refractive-index-high-dispersion glasscemented thereto as in a conventional fish eye lens system.

For the cemented surface in the doublet next to the aperture stop at theimage side thereof, the conventional lens design approach has onlyrequired achromatization by setting the refractive indices of the glasson the opposite sides of the cemented surface equal to each other, or ithas been used for correcting the Petzval sum in addition to theachromatization by setting the refractive power of the cemented surfacenegative. This lens design concept has been thought preferable indesigning fish eye lens systems since this design approach is alsofavorable to the correction of the field curvature and astigmatism.

In contrast thereto, the present invention has adopted a doublet havinga cemented surface of positive refractive power next to the aperturestop at the image side thereof. This novel concept of design achieves asatisfactory correction of sagittal flare, including Rinnen fehler, andcoma from zonal to marginal areas, which have been traditionally leftwithin the design parameters of compact high speed fish eye lens systemssuch as lens systems of F/2.8 in the prior art.

According to the present invention, the radius of curvature R of thecemented surface of the doublet next to the aperture stop, on the imageside thereof, is further required to be within the range from f to 3f asalready mentioned. If R is greater than 3f, positive coma and sagittalflare would be intolerably increased. On the other hand, a generation ofnegative coma and a negative deviation of Petzval sum would be caused,in designing a practical high speed fish eye lens system such as F/2.8,if R is less than f.

Each of the following Tables, set forth herein, are described relativeto a specific embodiment of the invention and relate directly to afigure. For example, Table 1 relates to Embodiment 1 and FIG. 1, withthe spherical aberrations being set forth in FIG. 2a, the astigmatism in2b, and distortion in 2c. Likewise, FIG. 3 relates to Embodiment 2 asset forth in Table 2. Correspondingly, the aberrations of Embodiment 2are set forth in FIGS. 4a, 4b and 4c. The other Tables, Embodiments andFigures are likewise related in sequential order.

                  TABLE 1                                                         ______________________________________                                        [Embodiment 1]                                                                f = 1, F/2.8, 2ω = 180°, back focal distance 2.324               Radius of Axial       Refractive   Abbe                                       Curvature Distance    Index        Number                                     ______________________________________                                        r.sub.1                                                                           4.7745                                                                                  d.sub.1                                                                             0.1299  N.sub.1                                                                            1.71300 ν.sub.1                                                                        53.93                            r.sub.2                                                                           0.8821                                                                                  d.sub.2                                                                             0.5688                                                    r.sub.3                                                                           1.6822                                                                                  d.sub.3                                                                             0.0938  N.sub.2                                                                            1.61800 ν.sub.2                                                                        63.38                            r.sub.4                                                                           0.8064                                                                                  d.sub.4                                                                             0.3313                                                    r.sub.5                                                                           1.6265                                                                                  d.sub.5                                                                             0.4838  N.sub.3                                                                            1.59551 ν.sub.3                                                                        39.23                            r.sub.6                                                                           -0.7284                                                                                 d.sub.6                                                                             0.0969  N.sub.4                                                                            1.62280 ν.sub.4                                                                        56.98                            r.sub.7                                                                           8.3331                                                                                  d.sub.7                                                                             0.0500                                                    r.sub.8                                                                           7.6334                                                                                  d.sub.8                                                                             0.1875  N.sub.5                                                                            1.80500 ν.sub.5                                                                        40.97                            r.sub.9                                                                           ∞                                                                                 d.sub.9                                                                             0.0806                                                    r.sub.10                                                                          ∞                                                                       (filter)  d.sub.10                                                                            0.0938  N.sub.6                                                                            1.58100 ν.sub.6                                                                        41.00                            r.sub.11                                                                          ∞                                                                                 d.sub.11                                                                            0.2413                                                    r.sub.12                                                                          -2.8724                                                                                 d.sub.12                                                                            0.0500  N.sub.7                                                                            1.59270 ν.sub.7                                                                        35.29                            r.sub.13                                                                          2.8034                                                                                  d.sub.13                                                                            0.2500  N.sub.8                                                                            1.64050 ν.sub.8                                                                        60.08                            r.sub.14                                                                          -1.1513                                                                                 d.sub.14                                                                            0.0063                                                    r.sub.15                                                                          3.2583                                                                                  d.sub.15                                                                            0.2919  N.sub.9                                                                            1.48749 ν.sub.9                                                                        70.15                            r.sub.16                                                                          -0.8827                                                                                 d.sub.16                                                                            0.0913  N.sub.10                                                                           1.80518 ν.sub.10                                                                       25.43                            r.sub.17                                                                          -1.7116                                                                   Σd = 3.0468                                                             ______________________________________                                    

                  TABLE 2                                                         ______________________________________                                        [Embodiment 2]                                                                f = 1, F/2.8, 2ω = 180°, back focal distance 2.294               Radius of Axial       Refractive   Abbe                                       Curvature Distance    Index        Number                                     ______________________________________                                        r.sub.1                                                                           4.7740                                                                                  d.sub.1                                                                             0.1299  N.sub.1                                                                            1.71300 ν.sub.1                                                                        53.93                            r.sub.2                                                                           0.8708                                                                                  d.sub.2                                                                             0.5688                                                    r.sub.3                                                                           1.6372                                                                                  d.sub.3                                                                             0.0938  N.sub.2                                                                            1.61800 ν.sub.2                                                                        63.38                            r.sub.4                                                                           0.8034                                                                                  d.sub.4                                                                             0.3313                                                    r.sub.5                                                                           1.5933                                                                                  d.sub.5                                                                             0.4838  N.sub.3                                                                            1.59551 ν.sub.3                                                                        39.23                            r.sub.6                                                                           -0.7261                                                                                 d.sub.6                                                                             0.0969  N.sub.4                                                                            1.62280 ν.sub.4                                                                        56.98                            r.sub.7                                                                           8.5127                                                                                  d.sub.7                                                                             0.2375  N.sub.5                                                                            1.80500 ν.sub.5                                                                        40.97                            r.sub.8                                                                           ∞                                                                                 d.sub.8                                                                             0.0806                                                    r.sub.9                                                                           ∞                                                                       (filter)  d.sub.9                                                                             0.0938  N.sub.6                                                                            1.58100 ν.sub.6                                                                        41.00                            r.sub.10                                                                          ∞                                                                                 d.sub.10                                                                            0.2413                                                    r.sub.11                                                                          -2.8722                                                                                 d.sub.11                                                                            0.0500  N.sub.7                                                                            1.59551 ν.sub.7                                                                        39.23                            r.sub.12                                                                          1.9923                                                                                  d.sub.12                                                                            0.2500  N.sub.8                                                                            1.65160 ν.sub.8                                                                        58.60                            r.sub.13                                                                          -1.1462                                                                                 d.sub.13                                                                            0.0063                                                    r.sub.14                                                                          3.3004                                                                                  d.sub.14                                                                            0.2919  N.sub.9                                                                            1.48749 ν.sub.9                                                                        70.15                            r.sub.15                                                                          -0.8687                                                                                 d.sub.15                                                                            0.0913  N.sub.10                                                                           1.80518 ν.sub.10                                                                       25.43                            r.sub.16                                                                          -1.7332                                                                   Σd = 3.0468                                                             ______________________________________                                    

                  TABLE 3                                                         ______________________________________                                        [Embodiment 3]                                                                f = 1, F/2.8, 2ω = 180°, back focal distance 2.213               Radius of Axial       Refractive   Abbe                                       Curvature Distance    Index        Number                                     ______________________________________                                        r.sub.1                                                                           4.1421                                                                                  d.sub.1                                                                             0.1299  N.sub.1                                                                            1.71300 ν.sub.1                                                                        53.93                            r.sub.2                                                                           0.7439                                                                                  d.sub.2                                                                             0.5688                                                    r.sub.3                                                                           1.4389                                                                                  d.sub.3                                                                             0.0938  N.sub.2                                                                            1.61800 ν.sub.2                                                                        63.38                            r.sub.4                                                                           0.7998                                                                                  d.sub.4                                                                             0.3313                                                    r.sub.5                                                                           7.0679                                                                                  d.sub.5                                                                             0.1250  N.sub.3                                                                            1.80500 ν.sub.3                                                                        40.97                            r.sub.6                                                                           ∞                                                                                 d.sub.6                                                                             0.0063                                                    r.sub.7                                                                           1.5149                                                                                  d.sub.7                                                                             0.3588  N.sub.4                                                                            1.59551 ν.sub.4                                                                        39.23                            r.sub.8                                                                           -0.7304                                                                                 d.sub.8                                                                             0.0969  N.sub.5                                                                            1.62280 ν.sub.5                                                                        56.98                            r.sub.9                                                                           4.4030                                                                                  d.sub.9                                                                             0.0806                                                    r.sub.10                                                                          ∞                                                                       (filter)  d.sub.10                                                                            0.0938  N.sub.6                                                                            1.58100 ν.sub.6                                                                        41.00                            r.sub.11                                                                          ∞                                                                                 d.sub.11                                                                            0.1875                                                    r.sub.12                                                                          -3.5894                                                                                 d.sub.12                                                                            0.0500  N.sub.7                                                                            1.58144 ν.sub.7                                                                        40.83                            r.sub.13                                                                          1.2959                                                                                  d.sub.13                                                                            0.2500  N.sub.8                                                                            1.63854 ν.sub.8                                                                        55.62                            r.sub.14                                                                          -1.0011                                                                                 d.sub.14                                                                            0.0063                                                    r.sub.15                                                                          3.1647                                                                                  d.sub.15                                                                            0.2919  N.sub.9                                                                            1.48749 ν.sub.9                                                                        70.15                            r.sub.16                                                                          -0.7778                                                                                 d.sub.16                                                                            0.0913  N.sub.10                                                                           1.80518 ν.sub.10                                                                       25.43                            r.sub.17                                                                          -1.9458                                                                   Σd = 2.7618                                                             ______________________________________                                    

                  TABLE 4                                                         ______________________________________                                        [Embodiment 4]                                                                f = 1, F/2.8, 2ω = 180°, back focal distance 2.261               Radius of Axial       Refractive   Abbe                                       Curvature Distance    Index        Number                                     ______________________________________                                        r.sub.1                                                                           4.4368                                                                                  d.sub.1                                                                             0.1299  N.sub.1                                                                            1.71300 ν.sub.1                                                                        53.93                            r.sub.2                                                                           0.7709                                                                                  d.sub.2                                                                             0.5688                                                    r.sub.3                                                                           1.3528                                                                                  d.sub.3                                                                             0.0938  N.sub.2                                                                            1.61800 ν.sub.2                                                                        63.38                            r.sub.4                                                                           0.7734                                                                                  d.sub.4                                                                             0.3313                                                    r.sub.5                                                                           1.3673                                                                                  d.sub.5                                                                             0.3588  N.sub.3                                                                            1.59551 ν.sub.3                                                                        39.23                            r.sub.6                                                                           -0.7178                                                                                 d.sub.6                                                                             0.0625  N.sub.4                                                                            1.62280 ν.sub.4                                                                        56.98                            r.sub.7                                                                           8.6559                                                                                  d.sub.7                                                                             0.2375  N.sub.5                                                                            1.80500 ν.sub.5                                                                        40.97                            r.sub.8                                                                           14.0377                                                                                 d.sub.8                                                                             0.0806                                                    r.sub.9                                                                           ∞                                                                       (filter)  d.sub.9                                                                             0.0938  N.sub.6                                                                            1.58100 ν.sub.6                                                                        41.00                            r.sub.10                                                                          ∞                                                                                 d.sub.10                                                                            0.1875                                                    r.sub.11                                                                          -2.8380                                                                                 d.sub.11                                                                            0.0500  N.sub.7                                                                            1.59551 ν.sub.7                                                                        39.23                            r.sub.12                                                                          1.9923                                                                                  d.sub.12                                                                            0.2188  N.sub.8                                                                            1.65160 ν.sub.8                                                                        58.60                            r.sub.13                                                                          -1.0701                                                                                 d.sub.13                                                                            0.0063                                                    r.sub.14                                                                          3.5704                                                                                  d.sub.14                                                                            0.2188  N.sub.9                                                                            1.48749 ν.sub.9                                                                        70.15                            r.sub.15                                                                          -0.8001                                                                                 d.sub.15                                                                            0.0625  N.sub.10                                                                           1.80518 ν.sub.10                                                                       25.43                            r.sub.16                                                                          -1.6272                                                                   Σd = 2.7006                                                             ______________________________________                                    

                  TABLE 5                                                         ______________________________________                                        [Embodiment 5]                                                                f = 1, F/2.8, 2ω = 180°, back focal distance 2.204               Radius of Axial       Refractive   Abbe                                       Curvature Distance    Index        Number                                     ______________________________________                                        r.sub.1                                                                           4.3046                                                                                  d.sub.1                                                                             0.1299  N.sub.1                                                                            1.71300 ν.sub.1                                                                        53.93                            r.sub.2                                                                           0.8034                                                                                  d.sub.2                                                                             0.5688                                                    r.sub.3                                                                           1.5151                                                                                  d.sub.3                                                                             0.0938  N.sub.2                                                                            1.61800 ν.sub.2                                                                        63.38                            r.sub.4                                                                           0.8390                                                                                  d.sub.4                                                                             0.3313                                                    r.sub.5                                                                           7.0679                                                                                  d.sub.5                                                                             0.1250  N.sub.3                                                                            1.80500 ν.sub.3                                                                        40.97                            r.sub.6                                                                           ∞                                                                                 d.sub.6                                                                             0.0063                                                    r.sub.7                                                                           2.0927                                                                                  d.sub.7                                                                             0.4838  N.sub.4                                                                            1.59270 ν.sub.4                                                                        35.29                            r.sub.8                                                                           -1.5780                                                                                 d.sub.8                                                                             0.1875  N.sub.5                                                                            1.60000 ν.sub.5                                                                        64.38                            r.sub.9                                                                           7.3459                                                                                  d.sub.9                                                                             0.0806                                                    r.sub.10                                                                          ∞                                                                       (filter)  d.sub.10                                                                            0.0938  N.sub.6                                                                            1.58100 ν.sub.6                                                                        41.00                            r.sub.11                                                                          ∞                                                                                 d.sub.11                                                                            0.2500                                                    r.sub.12                                                                          -4.7523                                                                                 d.sub.12                                                                            0.0500  N.sub.7                                                                            1.58144 ν.sub.7                                                                        40.83                            r.sub.13                                                                          1.2959                                                                                  d.sub.13                                                                            0.2500  N.sub.8                                                                            1.65844 ν.sub.8                                                                        50.88                            r.sub.14                                                                          -1.1273                                                                                 d.sub.14                                                                            0.0063                                                    r.sub.15                                                                          3.2103                                                                                  d.sub.15                                                                            0.3125  N.sub.9                                                                            1.48749 ν.sub.9                                                                        70.15                            r.sub.16                                                                          -0.8604                                                                                 d.sub.16                                                                            0.0913  N.sub.10                                                                           1.80518 ν.sub.10                                                                       25.43                            r.sub.17                                                                          -2.2499                                                                   Σd = 3.0606                                                             ______________________________________                                    

The preceding Tables 1-5 disclose five embodiments of the presentinvention which more than adequately establish the truthfulness of therecited ranges of conditions.

As can be readily appreciated, it is possible to deviate from the aboveembodiments of the present invention and as will be readily understoodby those skilled in the art, the invention is capable of manymodifications and improvements within the scope and spirit thereof.Accordingly, it will be understood that the invention is not limited bythe specific disclosed embodiments, but only by the scope and spirit ofthe appended claims.

I claim:
 1. A fish eye lens system comprising:a front lens groupconsisting of a pair of negative meniscus lens elements both convex tothe object side; an intermediate lens group consisting of a pair ofpositive lens elements and a negative lens element; and a rear lensgroup consisting of a pair of doublets, the object side one of whichincludes an intermediate cemented surface having a positive refractivepower.
 2. The invention of claim 1, wherein the radius of curvature R ofthe intermediate cemented surface of the object side doublet in the rearlens group fulfills the following condition wherein f represents thefocal length of the whole lens system:f<R<3f.
 3. The invention of claim1, wherein the focal length of the front lens group, f_(I), is definedas follows:2.7f<|f_(I) |<3.1fwherein f is the focal length of the wholelens system.
 4. The invention of claim 2 further comprising an aperturestop and an exchangeable filter both located between the intermediateand rear lens groups.
 5. The invention of claim 2 wherein one of thepair of positive lens elements is cemented to the negative lens elementin the intermediate lens group.
 6. The invention of claim 3, wherein thefocal length of the intermediate lens group, f_(II), is defined asfollows:2.6f<f_(II) <3.1f.
 7. The invention of claim 5, wherein theother of the pair of positive lens elements is located at the image sideof the cemented lens elements in the intermediate lens group.
 8. Theinvention of claim 5, wherein the other of the pair of positive lenselements is located at the object side of the cemented lens elements inthe intermediate lens group.
 9. The invention of claim 5, wherein all ofthe three lens elements are cemented together in the intermediate lensgroup.
 10. A fish eye lens system comprising:an aperture stop; a firstgroup of lens elements located at the object side of the aperture stop,including a pair of negative meniscus lens elements consecutivelyarranged at the front of the lens system; and a second group of lenselements located at the image side of the aperture stop including a pairof doublets, the image side one of the doublets including anintermediate cemented surface having a negative refractive power, whilethe object side one of the doublet being arranged next to the aperturestop and having an intermediate cemented surface fulfilling thefollowing conditions:φ>0 f<R<3fwherein: φ represents the refractivepower of the intermediate surface of the object side one of thedoublets; R represents the radius of curvature of the intermediatesurface of the object side one of the doublets; and f represents thefocal length of the whole lens system.
 11. An improved fish eye lenssystem comprising the following design parameters:

    ______________________________________                                        f = 1, F/2.8, 2ω = 180°, back focal distance 2.324               Radius of Axial       Refractive   Abbe                                       Curvature Distance    Index        Number                                     ______________________________________                                        r.sub.1                                                                           4.7745                                                                                  d.sub.1                                                                             0.1299  N.sub.1                                                                            1.71300 ν.sub.1                                                                        53.93                            r.sub.2                                                                           0.8821                                                                                  d.sub.2                                                                             0.5688                                                    r.sub.3                                                                           1.6822                                                                                  d.sub.3                                                                             0.0938  N.sub.2                                                                            1.61800 ν.sub.2                                                                        63.38                            r.sub.4                                                                           0.8064                                                                                  d.sub.4                                                                             0.3313                                                    r.sub.5                                                                           1.6265                                                                                  d.sub.5                                                                             0.4838  N.sub.3                                                                            1.59551 ν.sub.3                                                                        39.23                            r.sub.6                                                                           -0.7284                                                                                 d.sub.6                                                                             0.0969  N.sub.4                                                                            1.62280 ν.sub.4                                                                        56.98                            r.sub.7                                                                           8.3331                                                                                  d.sub.7                                                                             0.0500                                                    r.sub.8                                                                           7.6334                                                                                  d.sub.8                                                                             0.1875  N.sub.5                                                                            1.80500 ν.sub.5                                                                        40.97                            r.sub.9                                                                           ∞                                                                                 d.sub.9                                                                             0.0806                                                    r.sub.10                                                                          ∞                                                                       (filter)  d.sub.10                                                                            0.0938  N.sub.6                                                                            1.58100 ν.sub.6                                                                        41.00                            r.sub.11                                                                          ∞                                                                                 d.sub.11                                                                            0.2413                                                    r.sub.12                                                                          -2.8724                                                                                 d.sub.12                                                                            0.0500  N.sub.7                                                                            1.59270 ν.sub.7                                                                        35.29                            r.sub.13                                                                          2.8034                                                                                  d.sub.13                                                                            0.2500  N.sub.8                                                                            1.64050 ν.sub.8                                                                        60.08                            r.sub.14                                                                          -1.1513                                                                                 d.sub.14                                                                            0.0063                                                    r.sub.15                                                                          3.2583                                                                                  d.sub.15                                                                            0.2919  N.sub.9                                                                            1.48749 ν.sub.9                                                                        70.15                            r.sub.16                                                                          -0.8827                                                                                 d.sub.16                                                                            0.0913  N.sub.10                                                                           1.80518 ν.sub.10                                                                       25.43                            r.sub.17                                                                          -1.7116                                                                   Σd = 3.0468                                                             ______________________________________                                    


12. An improved fish eye lens system comprising the following designparameters:

    ______________________________________                                        f = 1, F/2.8, 2ω = 180°, back focal distance 2.29                Radius of Axial       Refractive   Abbe                                       Curvature Distance    Index        Number                                     ______________________________________                                        r.sub.1                                                                           4.7740                                                                                  d.sub.1                                                                             0.1299  N.sub.1                                                                            1.71300 ν.sub.1                                                                        53.93                            r.sub.2                                                                           0.8708                                                                                  d.sub.2                                                                             0.5688                                                    r.sub.3                                                                           1.6372                                                                                  d.sub.3                                                                             0.0938  N.sub.2                                                                            1.61800 ν.sub.2                                                                        63.38                            r.sub.4                                                                           0.8034                                                                                  d.sub.4                                                                             0.3313                                                    r.sub.5                                                                           1.5933                                                                                  d.sub.5                                                                             0.4838  N.sub.3                                                                            1.59551 ν.sub.3                                                                        39.23                            r.sub.6                                                                           -0.7261                                                                                 d.sub.6                                                                             0.0969  N.sub.4                                                                            1.62280 ν.sub.4                                                                        56.98                            r.sub.7                                                                           8.5127                                                                                  d.sub.7                                                                             0.2375  N.sub.5                                                                            1.80500 ν.sub.5                                                                        40.97                            r.sub.8                                                                           ∞                                                                                 d.sub.8                                                                             0.0806                                                    r.sub.9                                                                           ∞                                                                       (filter)  d.sub.9                                                                             0.0938  N.sub.6                                                                            1.58100 ν.sub.6                                                                        41.00                            r.sub.10                                                                          ∞                                                                                 d.sub.10                                                                            0.2413                                                    r.sub.11                                                                          -2.8722                                                                                 d.sub.11                                                                            0.0500  N.sub.7                                                                            1.59551 ν.sub.7                                                                        39.23                            r.sub.12                                                                          1.9923                                                                                  d.sub.12                                                                            0.2500  N.sub. 8                                                                           1.65160 ν.sub.8                                                                        58.60                            r.sub.13                                                                          -1.1462                                                                                 d.sub.13                                                                            0.0063                                                    r.sub.14                                                                          3.3004                                                                                  d.sub.14                                                                            0.2919  N.sub.9                                                                            1.48749 ν.sub.9                                                                        70.15                            r.sub.15                                                                          -0.8687                                                                                 d.sub.15                                                                            0.0913  N.sub.10                                                                           1.80518 ν.sub.10                                                                       25.43                            r.sub.16                                                                          -1.7332                                                                   Σd = 3.0468                                                             ______________________________________                                    


13. An improved fish eye lens system comprising the following designparameters:

    ______________________________________                                        f = 1, F/2.8, 2ω = 180°, back focal distance 2.213               Radius of Axial       Refractive   Abbe                                       Curvature Distance    Index        Number                                     ______________________________________                                        r.sub.1                                                                           4.1421                                                                                  d.sub.1                                                                             0.1299  N.sub.1                                                                            1.71300 ν.sub.1                                                                        53.93                            r.sub.2                                                                           0.7439                                                                                  d.sub.2                                                                             0.5688                                                    r.sub.3                                                                           1.4389                                                                                  d.sub.3                                                                             0.0938  N.sub.2                                                                            1.61800 ν.sub.2                                                                        63.38                            r.sub.4                                                                           0.7998                                                                                  d.sub.4                                                                             0.3313                                                    r.sub.5                                                                           7.0679                                                                                  d.sub.5                                                                             0.1250  N.sub.3                                                                            1.80500 ν.sub.3                                                                        40.97                            r.sub.6                                                                           ∞                                                                                 d.sub.6                                                                             0.0063                                                    r.sub.7                                                                           1.5149                                                                                  d.sub.7                                                                             0.3588  N.sub.4                                                                            1.59551 ν.sub.4                                                                        39.23                            r.sub.8                                                                           -0.7304                                                                                 d.sub.8                                                                             0.0969  N.sub.5                                                                            1.62280 ν.sub.5                                                                        56.98                            r.sub.9                                                                           4.4030                                                                                  d.sub.9                                                                             0.0806                                                    r.sub.10                                                                          ∞                                                                       (filter)  d.sub.10                                                                            0.0938  N.sub.6                                                                            1.58100 ν.sub.6                                                                        41.00                            r.sub.11                                                                          ∞                                                                                 d.sub.11                                                                            0.1875                                                    r.sub.12                                                                          -3.5894                                                                                 d.sub.12                                                                            0.0500  N.sub.7                                                                            1.58144 ν.sub.7                                                                        40.83                            r.sub. 13                                                                         1.2959                                                                                  d.sub.13                                                                            0.2500  N.sub.8                                                                            1.63854 ν.sub.8                                                                        55.62                            r.sub.14                                                                          -1.0011                                                                                 d.sub.14                                                                            0.0063                                                    r.sub.15                                                                          3.1647                                                                                  d.sub.15                                                                            0.2919  N.sub.9                                                                            1.48749 ν.sub.9                                                                        70.15                            r.sub.16                                                                          -0.7778                                                                                 d.sub.16                                                                            0.0913  N.sub.10                                                                           1.80518 ν.sub.10                                                                       25.43                            r.sub.17                                                                          -1.9458                                                                   Σd = 2.7618                                                             ______________________________________                                    


14. An improved fish eye lens system comprising the following designparameters:

    ______________________________________                                        f = 1, F/2.8, 2ω = 180°, back focal distance 2.261               Radius of Axial       Refractive   Abbe                                       Curvature Distance    Index        Number                                     ______________________________________                                        r.sub.1                                                                           4.4368                                                                                  d.sub.1                                                                             0.1299  N.sub.1                                                                            1.71300 ν.sub.1                                                                        53.93                            r.sub.2                                                                           0.7709                                                                                  d.sub.2                                                                             0.5688                                                    r.sub.3                                                                           1.3528                                                                                  d.sub.3                                                                             0.0938  N.sub.2                                                                            1.61800 ν.sub.2                                                                        63.38                            r.sub.4                                                                           0.7734                                                                                  d.sub.4                                                                             0.3313                                                    r.sub.5                                                                           1.3673                                                                                  d.sub.5                                                                             0.3588  N.sub.3                                                                            1.59551 ν.sub.3                                                                        39.23                            r.sub.6                                                                           -0.7178                                                                                 d.sub.6                                                                             0.0625  N.sub.4                                                                            1.62280 ν.sub.4                                                                        56.98                            r.sub.7                                                                           8.6559                                                                                  d.sub.7                                                                             0.2375  N.sub.5                                                                            1.80500 ν.sub.5                                                                        40.97                            r.sub.8                                                                           14.0377                                                                                 d.sub.8                                                                             0.0806                                                    r.sub.9                                                                           ∞                                                                       (filter)  d.sub.9                                                                             0.0938  N.sub.6                                                                            1.58100 ν.sub.6                                                                        41.00                            r.sub.10                                                                          ∞                                                                                 d.sub.10                                                                            0.1875                                                    r.sub.11                                                                          -2.8380                                                                                 d.sub.11                                                                            0.0500  N.sub.7                                                                            1.59551 ν.sub.7                                                                        39.23                            r.sub.12                                                                          1.9923                                                                                  d.sub.12                                                                            0.2188  N.sub.8                                                                            1.65160 ν.sub.8                                                                        58.60                            r.sub.13                                                                          -1.0701                                                                                 d.sub.13                                                                            0.0063                                                    r.sub.14                                                                          3.5704                                                                                  d.sub.14                                                                            0.2188  N.sub.9                                                                            1.48749 ν.sub.9                                                                        70.15                            r.sub.15                                                                          -0.8001                                                                                 d.sub.15                                                                            0.0625  N.sub.10                                                                           1.80518 ν.sub.10                                                                       25.43                            r.sub.16                                                                          -1.6272                                                                   Σd = 2.7006                                                             ______________________________________                                    


15. An improved fish eye lens system comprising the following designparameters:

    ______________________________________                                        f = 1, F/2.8, 2ω = 180°, back focal distance 2.204               Radius of Axial       Refractive   Abbe                                       Curvature Distance    Index        Number                                     ______________________________________                                        r.sub.1                                                                           4.3046                                                                                  d.sub.1                                                                             0.1299  N.sub.1                                                                            1.71300 ν.sub.1                                                                        53.93                            r.sub.2                                                                           0.8034                                                                                  d.sub.2                                                                             0.5688                                                    r.sub.3                                                                           1.5151                                                                                  d.sub.3                                                                             0.0938  N.sub.2                                                                            1.61800 ν.sub.2                                                                        63.38                            r.sub.4                                                                           0.8390                                                                                  d.sub.4                                                                             0.3313                                                    r.sub.5                                                                           7.0679                                                                                  d.sub.5                                                                             0.1250  N.sub.3                                                                            1.80500 ν.sub.3                                                                        40.97                            r.sub.6                                                                           ∞                                                                                 d.sub.6                                                                             0.0063                                                    r.sub.7                                                                           2.0927                                                                                  d.sub.7                                                                             0.4838  N.sub.4                                                                            1.59270 ν.sub.4                                                                        35.29                            r.sub.8                                                                           -1.5780                                                                                 d.sub.8                                                                             0.1875  N.sub.5                                                                            1.60000 ν.sub.5                                                                        64.38                            r.sub.9                                                                           7.3459                                                                                  d.sub.9                                                                             0.0806                                                    r.sub.10                                                                          ∞                                                                       (filter)  d.sub.10                                                                            0.0938  N.sub.6                                                                            1.58100 ν.sub.6                                                                        41.00                            r.sub.11                                                                          ∞                                                                                 d.sub.11                                                                            0.2500                                                    r.sub.12                                                                          -4.7523                                                                                 d.sub.12                                                                            0.0500  N.sub.7                                                                            1.58144 ν.sub.7                                                                        40.83                            r.sub. 13                                                                         1.2959                                                                                  d.sub.13                                                                            0.2500  N.sub.8                                                                            1.65844 ν.sub.8                                                                        50.88                            r.sub.14                                                                          -1.1273                                                                                 d.sub.14                                                                            0.0063                                                    r.sub.15                                                                          3.2103                                                                                  d.sub.15                                                                            0.3125  N.sub.9                                                                            1.48749 ν.sub.9                                                                        70.15                            r.sub.16                                                                          -0.8604                                                                                 d.sub.16                                                                            0.0913  N.sub.10                                                                           1.80518 ν.sub.10                                                                       25.43                            r.sub.17                                                                          -2.2499                                                                   Σd = 3.0606                                                             ______________________________________                                    